Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $69.53   5.714%   $73.5029   $73.50   $73.50   $73.50  
  Purchase #2 $238.61   9.675%   $261.6955   $261.70   $261.70   $261.70  
  Purchase #3 $117.87   8.549%   $127.9467   $127.95   $127.95   $127.90  
  Purchase #4 $157.68   4.375%   $164.5785   $164.58   $164.60   $164.60  
  Purchase #5 $142.84   3.125%   $147.3038   $147.30   $147.30   $147.30  
  Purchase #6 $34.30   9.209%   $37.4587   $37.46   $37.45   $37.50  
  Purchase #7 $15.76   6.844%   $16.8386   $16.84   $16.85   $16.80  
  7 purchase totals = $776.59       $829.3247   $829.33   $829.35   $829.30